Lots of different working styles. All the methods have practitioners who build story just fine. All of them are 'right'.
But before the Seat of the Pants . . . before The Extensive Outline . . how do we first approach story?
If I were handing out advice wholesale, (because, for instance, I didn't want to buckle down to work this morning,) I'd say to start writing before you know the story.
What it is --
dog much like the dog you might walk
These vignettes are a gift from your subconscious.
Don't be shy. Take the gift, already. Write the scenes out.
Of course, you're going to throw away most of this material. The beautiful scene is going to fall into backstory or it'll be off-stage or it simply won't happen.
But some of these scenes make it into the final manuscript. When they do, it's great. This is your primal story stuff. Your first visualization. Theses scenes paint your world.
Before you face that clean, empty screen with 'Chapter One', centered . . . catch as much as you can of the vivid and unexpected that bubbles up from the story yeasting in your mind.
Write the scenes, because they're freely given. As close as we get to 'inspiration'.
And because they give you momentum to write. They toss you into the current of story.
plotbunny at work
But these are static activities.
They aren't 'writing'.
'Writing' is immersion in the storytime with all its thought, feeling, motive, color, dialog, hitting tigers over the head, hot breath in the throat, dialog, walruses, and, y'know, dialog. 'Writing' is grabbing the scene as it runs past and riding it.
These lagniappe scenes toss you in the story river. They sweep you along. Now you're swimming. You're part of the story, not an observer.
Second advice is to build your characters' pasts before you necessarily know what they'll be up to in your current story.
I'm not talking about making a 'character profile' that sets down facts, though you can do that too. I'm saying to imagine little stories that happened to the characters before the WIP.
To take a case:
Sebastian and Adrian are weaving down a street in London, drunk. Singing. The action of the story opens.
But I knew where they'd been before the reader sees them in the alley in London, I had imagined other scenes of their lives. I knew how they'd met, years earlier in Paris, and nearly killed each other. I knew how they'd scuttled together out of France with the Secret Police two jumps behind.
So that's the second advice. Maybe you know what lies ahead of your character in the WIP, maybe not,
but he can walk into Line One, Page One, Chapter One, already in motion from his own story.